Nowadays, low-frequency standard radio waves containing time data (that is, a time code) are transmitted in various countries (for example, Germany, the United Kingdom, Switzerland, Japan, and so forth). In Japan, 40-kHz and 60-kHz low-frequency standard radio waves that have been subjected to amplitude modulation using a time code having a format shown in FIG. 12, are transmitted from two transmission facilities located in Fukushima Prefecture and Saga Prefecture). The time code comprises a plurality of frame is defined to have a time cycle of 60 seconds. According to FIG. 12, the time code is transmitted in a frame every time the figure representing the minute of an accurate time is updated (that is every minute).
Recently, so-called radio wave clocks that receive such time codes and correct time data of a timekeeping circuit based on the received time codes have been put into practical use. Besides, since the transmission frequencies of low-frequency standard radio waves to be transmitted from the two transmission facilities are different as described above, there have been provided radio wave clocks, which are adjusted to a so-called multi-band to become able to receive radio waves of both the frequencies (40 kHz and 60 kHz). Generally, such radio wave clocks are equipped inside with a straight receiving circuit adjusted to each frequency.
However, in order to make radio waves of two or more different frequencies receivable, it is necessary to prepare straight receiving circuits for the respective frequencies as described above. Therefore, there has arisen a problem that the circuit area and the amount of power consumption are increased. Further, a superheterodyne method has generally been used as a multi-frequency reception method. According to the superheterodyne method, it is necessary to change the local oscillation frequency in accordance with the frequency of a received radio wave.